Sedimentation processes caused by a modern tsunami have been discussed from the point of view of geologic and numerical investigations of the 1992 Flores tsunami in Indonesia.Geologic evidence on Babi Island shows an invasion of two waves with different direction and magnitude, which resulted in widespread deposition of marine sand on the north and south-southewest shores. On the latter, coarse and well-sorted carbonate sand with molluscan shells suggests that much more destructive waves swept across the southern coast as compared with the northern coast where the deposit included medium carbonate sand with a silty component.A physical explanation for such destructive waves on the southern coast of Babi is provided by a numerical simulation of the tsunami generation and propagation. The geologic and numerical results indicate that an isolated island surrounded by a circular shoreline or reef edge will be the hardest hit on the coast on the back side of the island relative to the tsunami source.